740 The Role of SMAD Signaling in the Pathogenesis of Pain in Chronic Pancreatitis

Introduction: Interleukin 9 is a pleiotropic pro-inflammatory cytokine mainly produced by T cells, beside B cells and mast cells. Mounting evidence suggests that there may be a specialized subset of T cells dedicated to produce IL-9 which are so called Th9 cells. In these cells the IL-9 gene is regulated by transcription factors like PU.1 and IRF4. Also many cytokines have been investigated so far in experimental models of chronic intestinal inflammation, the role of IL-9 is largely unidentified. But high concentrations of IL-9 in the colon tissue during colitis reveal the important role of this cytokine. Methods: For the analysis of IL-9 in the development of chronic intestinal inflammation IL-9 deficient mice were used in oxazolone-colitis model. Miniendoscopic analysis has been done to monitor the manifestation of the colitis. The inflamed colon was isolated and histological sections were taken for immunohistofluorescent staining and real-time PCR analysis. For therapeutically treatment wildtype mice were given 40μg of specific anti IL-9 antibody to prevent the emergence of colitis. Results: In the experimental oxazolone-colitis model the IL-9KO mice were protected. This became evident in the miniendoscopic analysis and in the HE staining. Immunofluorescence staining shows a decrease of the IL-9 regulating transcription factor PU.1 in the IL-9 deficient mice, indicating the involvement of PU.1 in the IL-9 production. This is consistent with the fact that PU.1 is higher expressed in human biopsies of colitis patients, which illustrates the pro-inflammatory role of IL-9 in patients suffering from inflammatory bowel disease. Double staining of CD4+ and PU.1 and EPCAM and PU.1 respectively suggests that there are specialized T cells expressing the transcription factor PU.1 implying a role of Th9 cells in colitis. Further analysis of the pro-inflammatory effect of IL-9 showed that the blockage of high IL-9 concentrations with a specific anti IL-9 antibody in wildtype mice lead to a protection in oxazolone-colitis model. Conclusion: Here, we have identified a central pathogenic role for Th9 cells in chronic intestinal inflammation. This is based on the fact that IL-9 is increased in inflamed colon tissue and IL-9KO mice are protected in the experimental oxazolone-colitis model. Furthermore, administration of a blocking anti IL-9 antibody before the manifestation of colitis has a protective effect. Thus IL-9 emerges as a potentially new therapeutic target for inflammatory bowel diseases.